Process and apparatus for the manufacture of high tension cables



United States Patent O 3,95,069 PRGCESS AND APARA'FUS FR THE MANU- FACZFURF. F HGH TENSN CAEJES Panic Grezzana Priaroggia, Milan, italy, assigner to Pirelii Societa per Azioni, Miian, italy, a corporation of Itaiy Fiied lian. 25', i952, Ser. No. 84,844 Claims priority, appiication Itaiy, Feb. 5, 1960, 2,1386/69 The present invention relates to the manufacture of high-tension electric cables insulated with layers of paper impregnated with a thick oil or a suitable compound, such as mineral oil and rosin or polyisobutylene.

These cables are of the pipe type, namely are devoid of the outer metal sheath adherent to their insulation and are designed to be drawn within metal pipes, for instance steel pipes, the interspace between the cable and the pipe being then lled with insulating oil under pressure (cables of the oil-pressure type) or with an inert gas under pressure (cables of the gas-pressure type). More precisely, the present invention refers to an improved process and to the corresponding plant for the application of the screening tapes and, subsequently, of the skid Wire or wires about the insulation of impregnated paper of the pipe type cables.

At the present state of the art, the manufacturing process of the above mentioned cables comprises the following operations:

(l) The normal paper insulation is applied on the cable conductor in superposed layers by means of suitable taping machines; then, if required, an electric screening is carried out by helically winding one or more semi-conductive layers, for instance of carbon paper; the so obtained cable core is then taken up on a metal bobbin which is introduced into a suitable vacuum-tight metal tank, provided with a steam jacket or coil for its heating;

(2) The cable core is dried by heating under vacuum and is impregnated with a previously degassed iiuid which is admitted into the tank under vacuum; then the suction from the tank is interrupted and the tank is placed under static pressure with the impregnating fluid therein.

If a cable within a steel pipe under oil pressure, namely one with a completely impregnated insulation, is to be manufactured, the impregnating uid under static pressure is at iirst cooled and then the tank, before being opened, is brought to the atmospheric pressure.

if instead a gas-pressure cable, namely one with a partially impregnated insulation, is to be mariuiacmred, the impregnating fluid while still at a high temperature, is evacuated from the tank under pressure of an inert gas, the core is allowed to drain under gas pressure for a certain period of time, in this case reheating the tank for this purpose, and the tank, before being opened, is brought to the atmospheric pressure.

(3) The bobbin carrying the impregnated cable core is removed from the tank and is placed behind the taping machine which applies to the core a screening constituted, for instance, by tapes of synthetic material, such as polyethylene-terephthalate, and/ or by tapes of the same material but metallized on one face, for instance, with a very thin layer of aluminum, and iinaliy a copper tape is applied.

The same taping machine or a similar machine subsequently applies one or two skid wires, namely one or two metal strips having a thickness of 4 5 min. and a D-sbaped section, which are helically wound about the cable core with their curved portion towards the outside and with a somewhat long pitch (5-10 cm.).

The above described process, hereinbefore used, shows the serious inconvenience that, during the handling of the cable core from the tank to the taping machine and the 6 Claims.

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application of the screening tapes, the insulation is exposed to air for a more or less long period of time, with a consequent absorption of moisture and with a harmful effect on its dielectric characteristics.

The present invention has the aim of eliminating the above cited inconvenience, of reducing the total time required for the drying, impregnating and taping operations, and of increasing the output of the plant by virtue of the particular disposition of the plant itseif.

To this end recourse is made to the adoption of drying and impregnating, stainless steel tanks, preferably of the vertical type, namely able to encase a metal bobbin rotatable about its own horizontal axis, and provided with a lateral tubular extension.

These tanks, already known, are described in the United States Patent No. 3,013,912 of the same applicant and will be referred to in the following description.

The object ofthe present invention is a process and plant for the manufacture of high-tension electric cables to be laid within metal pipes, and concerns the application of screening tapes and of one or two skid wires on the impregnated cable cores in such a way that their insulation must not absorb moisture from the air prior to the application of the tapes and skid wires.

The process provides jthe direct passage of the irnpregnated core from the impregnating tank to the taping machine under .an atmosphere of inert gas, such as nitrogen; furthermore the taping operations on a core length are carried out separately, but at the same time as the drying and impregnating operations on other core lengths so that, by virtue of the particular disposition of the plant, the total time required for the manufacture of the pipe cables is considerably shortened.

The plant forming the object of the present invention comprises an impregnating tank having a lateral tubular extension situated near, and directed towards, the taping machine, said extension being provided with a connecting tube which extends as far as the rear side of the first taping head and is opened at that end.

The piant also includes several adjacent impregnating tanks, for instance three, disposed in side-by-side alignment, a taping machine which, together with the means for drawing the cable core, is assembled on a truck running on rails along the face of the tanks, and at least a supporting stand for `the take-up bobbin of the finished cable, disposed at the side opposite to the tanks with respect t0 the assembly constituted by the taping machine and by the drawing means.

A schematic, plan view of a preferred embodiment of the plant of the invention is illustrated in the single figure or" the attached drawing.

For a better understanding of the present invention, the description of the process is given before that of the plant. First of all the cable conductor is bared at the two ends of the core and an insulated metal strand, called a connecting hawser, is fastened on each end by means of a suitable connector tightened onto it.

The hawsers, together with the cable core, are previously wound on the metal bobbin in superposed cylindrical layers, coaxial with the bobbin, and serve to convey the electric current to the conductor to heat it at least in the initial stage of the drying under vacuum. Therefore, the head hawser is connected, at its free end, with a termnal situated on the flanged head of the tubular extension, while the tail hawser has its free end connected with the other terminal situated on the ilange of the metal bobbin, and must have a length suiiicient to allow the taping ofthe whole impregnated cable core without the need of detaching it from its corresponding terminal.

When the bobbin carrying the cable core, with the associated connecting hawsers, is placed into the tank, it is subiected toa hot dryingunder vacuumrand then to an impregnation with a degassed insulating fluid which is admitted into the tank still under vacuum, the heating being subsequently interrupted. Once the tank is lled,

the suction is interrupted and the tank is subjected to a static pressure with the insulating uid therein.

If it is necessary to manufacture a cable of the type drawn into a steel pipeunder oil pressure, the impregnating iiuid is allowed to cool under static pressure within the tank until it isy brought to the room temperature; then when the tank is brought to the atmospheric pressure, the level of impregnating fluid is lowered to the extent necessary to permit opening of the tank and a ow of inert gas, such as, for instance, nitrogen, is admitted into the tank so that during the next operation step the entrance of moisture into the tank is avoided.

On the other hand, if it is necessary to manufacture a gas-pressure type cable, the impregnating fluid is completelyevacuated from the tank under pressure of inert gas at a still high temperature, the iluid is allowed to drain into the bottom of the tank for a certain period of time still under gas pressure, heating, if required, the tank with steam, and then the tank, before being opened, is. brought to the atmospheric pressure.

At this point, the process forming the object of the present invention is started. It consists in directly drawing the cable core, which is payed 01T from the bobbin within the tank, to the taping machine situated in front of and in proximity to the tank, and in maintaining it, during its travel, under an atmosphere of inert gas (nitrogen). For this purpose the fianged head of the tubular extension of the tank is removed, the end of the head hawser is detached from its corresponding terminal and is connected to a metal rope, called pulling rope, which serves to draw the cable core out of the tank and to lead it, through a connecting tube, to the taping machine. At the same time nitrogen is continuously admitted into the tank so as to have a slight flow of gas from the tank interior to the open end of the tube, which is disposed behind the rst taping head. Then the core is taped in the conventional way, the cable insulation being prevented from coming in contact with the air.

A typical example of the taping operation is given by a machine provided with three taping heads, which successively applies:

(a) Two screening tapes of metallized synthetic material, intercalated to each other and wound up helically, for instance in a left-handed sense;

(b) A copper tape and a tape of metallized synthetic material, intercalated to each other and wound up helically, in this case in a right-handed sense;

(c) One or two skid wires, also intercalated to each other and wound up helically, in this case in a left-handed sense (double-thread application).

The plant forming the object of the present invention is illustrated in plan view in the attached gure. It comprises three irnpregnating tanks of the above described known type, indicated with the reference numerals 1', 1" and 1"', and provided with tubular extensions 2', 2" and 2"'. The tanks are disposed in side-by-side alignment and in front of them there is the assembly constituted by the taping machine 4 and by the drawing means 5 which is mounted on a truck 6 running on rails 7 aligned in the same direction as the tanks.

The figure represents the tank 1' in operation. The iirst taping head d' (a pair of supports for rolls `or bob* bins) of the machine is near the end of the tubular extension 2' of the tank. Said end is in gas-tight connection with a connecting pipe or tube 3, carried for instance by the taping machine and movable with it, which tube 3 extends as far as the rear side of the first taping head 4', where it is open to the atmosphere.

At the opposite side of each tank with respect to the assembly constituted by the taping machine and by the drawing means, there are three stationary stands for the support of the take-up bobbins 8', 8" and 8" of the finished cable. However a single bobbin 8', mounted on an independent truck 9 could be provided, which truck 9 may also be used for carrying the iinished cable inside the factory. Alternatively, the bobbin 8' may be mounted on an extension of the truck 6.

By means of the above described arrangement, the taping machine and the drawing means can be moved from one tank to another so that, during the taping on the cable core coming out from one tank, two other core lengths can be dried and impregnated in the adjacent tanks.

Moreover, by means of a suitable phase displacement in star-ting the drying operation Within the single tanks, its is possible to keep the taping machine in substantially continuous operation which permits a considerable increase of the plant output with respect to the case in which each tank is coupled with its own taping machine and a drawing means.

The taping heads of the machine can be in any desired number; however, it is convenient to reduce said number to three, or at the most four, one of which is a spare, in order to limit the axial dimensions of the taping machine. The figure of the'drawing represents a machine with three taping heads 4', 4" and 4"'.

The drawing means 5 can be a capstan but, to reduce the overall size, it ispreferable to yad-opt a rectilinear means (caterpillar). From the drawing it is apparent that the third taping head 4"' can `apply simultaneously two skid Wires intercalated to each other. The above mentioned pulling rope, wound up at one end on the capstan or disposed between the jaws of the caterpillar, runs through the whole length of the taping machine, passes within the connecting tube 3 and at the other end can be fastened at the right moment to the end of the head hawser of each core length. Then the connecting tube 3 is secured in gas-tight relation to the end of the tubular extension 2', or 2" or 2"'.

By operating the drawing means, the pulling rope, through the head hawser, acts on the cable core, compelling it to be paid otf from the bobbi-n and to come out of the tank, the cable core remaining well stretched during the taping operation by means of Ia brake disposed inside the tank.

The present invention is not limited to the above described and illustrated form of realization, but it is understood that possible modifications can be provided Without falling out of the scope of the invention itself.

What I claim is:

'1. A process for the manufacture of a high-tension electric cable having a conductive core encircled by insulation which is covered by a protective layer, said process comprising the steps of drying a length of cable Without the protective layer thereon under vacuum at a first,

enclosed position and impregnating said length with an insulating tuid at said position, transferring said length from said rst position to a second position spaced from said iirst position while winding said protective layer on said length at said second position and surrounding the portion of said length intermediate said tirst and second positions with a ow of a dry inert gas whereby the insulation of said portion is maintained out of contact with air during its passage betweeen said first and second positions. Y

v2. Av` process for the manufacture of lengths of high tension electric cable, each length having a conductive core encircled by insulation which is covered by a protective layer, with apparatus comprising a plurality of adjacent drying and impregnating tanks and a Winding apparatus disposed to wind the protective layer on each length of cable as it is removed from the tank in which it is dried and impregnated, said process comprising drying lengths of cable Without the protective layer thereon under vacuum in saidtanks, one length in each tank, and impregnating the lengths in said tanks with an insulating fluid, transferring said lengths succes-sively from said tanks to said winding apparatus while winding said protective layer thereon, surrounding the portion of each length intermediate the tank from which it is Vtransferred and the winding apparatus with a ilow of a dry inert gas so as to maintain said portion out of contact with air during its passage between the tank and the winding ap paratus, and controlling the drying and impregnating of said lengths so that successive lengths are dried and impregnated while the protective layer is being wound on a preceding length and so that successive lengths are ready for the Winding of said protective layer thereon when the winding of a preceding length is completed whereby the Winding apparatus may be kept in substantialiy continuous operation except for the time required to feed a succeeding length to the Winding apparatus after the completion of 'the winding of the protective layer on a preceding length.

3. Apparatus for the manufacture of high-tension electric cables comprising a plurality of cable treating tanks for receiving cable lengths to be treated, each tank being closed to the atmosphere except for an opening therein for the removal of a cable length therethrough and said tanks being disposed with said openings facing in the same direction, a plurality of aligned strip winding heads for Winding strips around a cable length, said heads being mounted on a truck movable transversely with respect to said direction for seiectiveiy aligning said heads with the opening in each of said tanks, means for drawing a cable length through said openings and through said heads mounted on said truck with said heads between said drawing means and said tanks, a pipe through which a cable length may be drawn and adapted to be connected to a tank in alignment with the opening therein, said pipe extending from a tank to the one of said heads nearest said last-mentioned tank, and means for supplying an inert gas to the tank to which said pipe is connected and to the interior of said pipe during the removal of a cable length through the opening in said last-mentioned tank.

4. Apparatus for the manufacture of high tension cables having a conductive core encircled by insulation which is covered by a protective layer, said apparatus comprising -a plurality of vacuum and impregnating tanks mounted in side-by-side relation, each of said tanks being adapted to receive an uniinished length of said cable Without lthe protective layer but with the core and insulation and each tank having an opening therein for removal of said cable length therefrom, means for evacuating said tanks and supplying a cable impregnating tiuid thereto, a Winding head exterior to said tanks for Winding said protective iayer on an uniinished cable length, means movably mounting said head .adjacent said tanks and for selectively positioning said head in alignment with the opening in each of said tanks, and means for drawing a cable length through said opening and said head.

5. Apparatus as set forth in claim d, wherein said tanks are disposed with said openings facing in the same direction and said head and said drawing means are mounted on a truck movable in `a direction extending transversely to said first-mentioned direction.

6. Apparatus according to claim 5 further comprising a gastight tube extending between the tank adjacent said truck and said winding head, said tube having a gas-tight connection at one end with said last-mentioned tank and having its interior in alignment with said opening, Whereby the interior of said tube is in gas communication with the interior of said last-mentioned tank, yand said tube being open at its other end and means for Supplying an inert gas under pressure above atmospheric pressure to the interior of said tanks, whereby said gas lsurrounds the cable length and tiows outwardly of the open end of said tube.

References Cited by the Examiner UNITED STATES PATENTS 1,917,957 7/33 Ell.

2,065,927 12/36 Scott 117-115 2,55,403 4/39 Cook.

2,345,864 4/ 44 Arnold 156-56 2,893,061 7/59 Terry 18-59 2,986,486 5/61 Short 18--59 FOREIGN PATENTS 414,765 S/ 34 Great Britain.

ALEXANDER WYMAN, Primary Examiner.

EARL BERGERT, CARL F. KRAFT, Examiners. 

1. A PROCESS FOR THE MANUFACTURE OF A HIGH-TENSION ELECTRIC CABLE HAVING A CONDUCTIVE CORE ENCIRCLED BY INSULATION WHICH IS COVERED BY A PROTECTIVE LAYER, SAID PROCESS COMPRISING THE STEPS OF DRYING A LENGTH OF CABLE WITHOUT THE PROTECTIVE LAYER THEREON UNDER VACUUM AT A FIRST ENCLOSED POSITION AND IMPREGNATING SAID LENGTH WITH AN INSULATING FLUID AT SAID POSITION, TRANSFERRING SAID LENGTH FROM SAID FIRST POSITION TO A SECOND POSITION SPACED FROM SAID FIRST POSITION WHILE WINDING SAID PROTECTIVE LAYER ON SAID LENGTH AT SAID SECOND POSITION AND SURROUNDING THE PORTION OF SAID LENGTH INTERMEDIATE SAID FIRST AND SECOND POSITIONS WITH A FLOW OF A DRY INERT GAS WHEREBY THE IN- 